Abstract : Childhood Absence Evolving to Juvenile Myoclonic Epilepsy (CAE/JME) is an uncommon form of genetic generalized epilepsy that appears as absence in childhood and evolves into generalized ... [more ▼]

Abstract : Childhood Absence Evolving to Juvenile Myoclonic Epilepsy (CAE/JME) is an uncommon form of genetic generalized epilepsy that appears as absence in childhood and evolves into generalized tonic–clonic seizures with myoclonic jerks during adolescence. In some family of patients affected by CAE/JME, mutations have been observed in the gene encoding for the transport protein importin-8 (IPO8). IPO8 could be at the origin of CAE/JME via its role in the transport of its targets (like Ago-2, Smad4, c-Jun). RT-qPCR has shown that IPO8 mRNA is expressed at all ages with no big difference in expression level. Using ISH, a clear expression of mIPO8 mRNA was observed in the sub-ventricular/ventricular zone (SVZ/VZ), the cortical plate (CP) and the ganglionic eminences (GE) of developing brain at E14. Both SVZ/VZ and GE are the “neurogenic niches” that generate glutamatergic and GABAergic neurons respectively. The implication of IPO8 in the generation of “glutamatergic neurons” was investigated by In Utero electroporation (IUE) and MGE Electroporation. Using shRNA, we observed that after 3 days, “glutamatergic neuroblasts” do not reach the CP in contrast to the control condition. This effect can be rescued by the co-expression of a form of IPO8 that is resistant to the shRNA. When overexpressing the pathological forms of hIPO8, but not a variant, migration of “glutamatergic neuroblasts” was also impaired. However, when the observation is made later, i.e. at P5, we observed that the neuroblasts finally reach their correct layer in the cortex, suggesting IPO8 only delayed but not blocked migration. Moreover, shRNA against IPO8 mRNA lead to alteration of interneurons (GABAergic neurons) migration same to overexpression of one mutated form of IPO8. Conclusion : IPO8 is expressed in mouse brain during development. It shows a clear expression during embryogenesis in the “neurogenic niches”. Moreover, IPO8 modulates neuroblasts (radial and tangential) migration in the developing brain. So, abnormal brain development due to IPO8 mutations could be at the origin of CAE/JME. [less ▲]

Thiamine is essential for normal brain function and its deficiency causes metabolic impairment, specific lesions, oxidative damage and reduced adult hippocampal neurogenesis (AHN). Thiamine precursors with increased bioavailability, especially benfotiamine, exert neuroprotective effects not only for thiamine deficiency (TD), but also in mouse models of neurodegeneration. As it is known that AHN is impaired by stress in rodents, we exposed C57BL6/J mice to predator stress for 5 consecutive nights and studied the proliferation (number of Ki67-positive cells) and survival (number of BrdU-positive cells) of newborn immature neurons in the subgranular zone of the dentate gyrus. In stressed mice, the number of Ki67- and BrdU-positive cells was reduced compared to non-stressed animals. This reduction was prevented when the mice were treated (200 mg/kg/day in drinking water for 20 days) with thiamine or benfotiamine, that were recently found to prevent stress-induced behavioral changes and glycogen synthase kinase-3β (GSK-3β) upregulation in the CNS. Moreover, we show that thiamine and benfotiamine counteract stress-induced bodyweight loss and suppress stress-induced anxiety-like behavior. Both treatments induced a modest increase in the brain content of free thiamine while the level of thiamine diphosphate (ThDP) remained unchanged, suggesting that the beneficial effects observed are not linked to the role of this coenzyme in energy metabolism. Predator stress increased hippocampal protein carbonylation, an indicator of oxidative stress. This effect was antagonized by both thiamine and benfotiamine. Moreover, using cultured mouse neuroblastoma cells, we show that in particular benfotiamine protects against paraquat-induced oxidative stress. We therefore hypothesize that thiamine compounds may act by boosting anti-oxidant cellular defenses, by a mechanism that still remains to be unveiled. Our study demonstrates, for the first time, that thiamine and benfotiamine prevent stress-induced inhibition of hippocampal neurogenesis and accompanying physiological changes. The present data suggest that thiamine precursors with high bioavailability might be useful as a complementary therapy in several neuropsychiatric disorders. [less ▲]

Importin-8 (IPO8) is a protein that regulates the nucleocytoplasmic transport of some proteins important for cerebral development (Ago2, c-Jun, Smad4). In HEK cells, IPO8 seems to not plays others roles ... [more ▼]

Importin-8 (IPO8) is a protein that regulates the nucleocytoplasmic transport of some proteins important for cerebral development (Ago2, c-Jun, Smad4). In HEK cells, IPO8 seems to not plays others roles (like mitotic spindle formation, primary cilium transport). In situ hybridization performed in mouse brains slices shows that IPO8 is already expressed at E14. Moreover, inhibition of its action (IPO8) in embryonic mouse brain leads to impairment of neuroblast migration to upper cortical layers. IPO8 could then be at the origin of some pathologies with neuronal migration deficit. [less ▲]

Jeavons syndrome (JS) is an uncommon form of juvenile epilepsy. In some family affected by JS, the gene of importin-8 (IPO8) a member of karyopherin superfamily of proteins, has been found mutated ... [more ▼]

Jeavons syndrome (JS) is an uncommon form of juvenile epilepsy. In some family affected by JS, the gene of importin-8 (IPO8) a member of karyopherin superfamily of proteins, has been found mutated. Karyopherin are known to regulate nucleo-cytoplasmic transport of many proteins. IPO8, a member of the β-karyopherin sub-family, is reported to control the transport Ago-2, c-Jun and Smad-4 for example, three proteins important for brain development. Here, we show that IPO8 is well expressed in mouse brain at embryonic stage. Moreover inhibition of IPO8 mRNA by shRNA in-utéro-electroporation (IUE), impairs early neuroblast migration as weel as IUE overexpression of mutated form of human IPO8. So, abnormal brain development due to IPO8 mutations could be at the origin of Jeavons Syndrome, Chilhood abscence evolving (CAE) and/or juvenile myoclonic epilepsy (JME). [less ▲]

Regulation of nucleocytoplasmic transport of proteins by the karyopherin superfamily is critical for cell physiology as it controls mainy fundamental processes such as division, differenciation, migration ... [more ▼]

Regulation of nucleocytoplasmic transport of proteins by the karyopherin superfamily is critical for cell physiology as it controls mainy fundamental processes such as division, differenciation, migration, adaptation to external environment etc. Beside this fundamental role, ß1 and ß2 members of this superfamily are also implicated in mitosis and ciliary entry respectively. Importin-8 (IPO8), a member of the β-karyopherin family, is reported to control the transport Ago-2, c-Jun and Smad-4 for example, three proteins important for brain development. First, we have verify the subcellular localisation of IPO8 in HEK and hTert cells. No colocalisation with either the mitotic spindle or the primary cilia could be observed. So it seems IPO8 only plays a role in nuclear transport of proteins. Then we have assessed the expression of IPO8 in mouse brain by In Situ Hybridization at various embryonic (E12, E14, E18) and post natal age (P5, P60). A strong expression was observed during embryonic stages, and especially in the ventricular zone and the cortical plate of the cerebral cortex and the ganglionic eminences both at E14. Therefore, the implication of IPO8 in the radial migration has been assessed by in utero electroporation of shRNA at E14. Three days after IUE, we observed that neuroblast accumulates in the Intermediate zone (IZ) and do not reach the cortical plate (CP) in constrast to the control condition. This effect can be corrected by coexpressing a form of IPO8 that is not targeted by the shRNA, demonstrating the specificity of the effect. In conclusion, regarding its role in transport, IPO8 could modulate neurons migration in the developing brain and could be also at the origin of some diseases associated with neurons migration defects. [less ▲]

Juvenile myoclonic epilepsy is one of the most common forms of generalized genetic epilepsy. Genetic studies have shown that heterozygous mutations in Myoclonin1 are responsible for 3-9% of clinical cases ... [more ▼]

Juvenile myoclonic epilepsy is one of the most common forms of generalized genetic epilepsy. Genetic studies have shown that heterozygous mutations in Myoclonin1 are responsible for 3-9% of clinical cases worldwide. This protein contains three DM10 domains of unknown function and an EF-hand domain. We have previously demonstrated that Myoclonin1 is a microtubule-associated protein involved in cell division and radial migration during neocortex development. In cells, this protein co-localized with specific structures rich in microtubules (MTs) such as the centrosome, the poles of the mitotic spindle or the motile cilia but not with cytoplasmic MTs. This suggests post-translational modifications (PTM) of MTs may be important for the interaction between Myoclonin1 and MTs. We have co-express the different enzymes catalyzing PTM of MTs with Myoclonin1 in U2OS cell line. With one of these enzymes, we observed a strong increase in PTM in the presence of Myoclonin-1. This suggests that Myoclonin1 may interact with and modulate the activity of this enzyme. By using luciferase complementation assay and pull down experiments, we could demonstrate that it is indeed the case. Interestingly, the effect is observed even when a DM10 domain alone is co-expressed with the enzyme, suggesting for the first time a role for this domain. In conclusion our data suggest myoclonin-1 modulates specific PTM of MTs. This is of prime importance for microtubule dynamic and notably for neuroblast precursor migration during neocortex development. This could be the mechanism that explains why pathological forms of myoclonin-1 affect brain development. [less ▲]

Rationale: Juvenile myoclonic epilepsies (JME) are one of the most common forms of genetic generalized epilepsy. Genetic studies have shown that heterozygous mutations in EFHC1/Myoclonin1 are responsible ... [more ▼]

Rationale: Juvenile myoclonic epilepsies (JME) are one of the most common forms of genetic generalized epilepsy. Genetic studies have shown that heterozygous mutations in EFHC1/Myoclonin1 are responsible for 3-22% of JME cases worldwide. The Myoclonin1 protein contains three DM10 domains of unknown function and an EF-hand domain. We have previously demonstrated that Myoclonin1 is a microtubule-associated protein involved in cell division and radial migration during neocortex development. In cells, this protein co-localized with specific structures rich in microtubules (MTs) such as the centrosome, the poles of the mitotic spindle or the motile cilia but not with cytoplasmic MTs. This suggests post-translational modifications (PTM) of MTs may be important for the interaction between Myoclonin1 and MTs Methods: We co-expressed the different enzymes catalyzing PTM of MTs with Myoclonin1 in U2OS cell line, and then performed immunocytochemistry and western blot analysis. We next performed pulldown and luciferase complementation assays to test protein interaction Results: With one of these enzymes, we observed a strong increase in PTM in the presence of Myoclonin- 1.Interestingly, the effect is observed even when a DM10 domain alone is co-expressed with the enzyme, suggesting for the first time a role for this domain. This suggests that Myoclonin1 may interact with and modulate the activity of this enzyme. By using luciferase complementation assay and pull down experiments, we could demonstrate that both proteins interact. Conclusions: Our data suggest Myoclonin-1 modulates specific PTM of MTs. This is of prime importance for microtubule dynamic and notably for neuroblast precursor migration during neocortex development. This could be the mechanism that explains why pathological forms of myoclonin-1 may affect brain development. [less ▲]

Juvenile myoclonic epilepsy is one of the most common forms of generalized genetic epilepsy. Genetic studies have shown that heterozygous mutations in Myoclonin1 are responsible for 3-9% of clinical cases ... [more ▼]

Juvenile myoclonic epilepsy is one of the most common forms of generalized genetic epilepsy. Genetic studies have shown that heterozygous mutations in Myoclonin1 are responsible for 3-9% of clinical cases worldwide. This protein contains three DM10 domains of unknown function and an EF-hand domain. We have previously demonstrated that Myoclonin1 is a microtubule-associated protein involved in cell division and radial migration during neocortex development. In cells, this protein co-localized with specific structures rich in microtubules (MTs) such as the centrosome, the poles of the mitotic spindle or the motile cilia but not with cytoplasmic MTs. This suggests post-translational modifications (PTM) of MTs may be important for the interaction between Myoclonin1 and MTs. We have co-express the different enzymes catalyzing PTM of MTs with Myoclonin1 in U2OS cell line. With one of these enzymes, we observed a strong increase in PTM in the presence of Myoclonin-1. This suggests that Myoclonin1 may interact with and modulate the activity of this enzyme. By using luciferase complementation assay and pull down experiments, we could demonstrate that it is indeed the case. Interestingly, the effect is observed even when a DM10 domain alone is co-expressed with the enzyme, suggesting for the first time a role for this domain. In conclusion our data suggest myoclonin-1 modulates specific PTM of MTs. This is of prime importance for microtubule dynamic and notably for neuroblast precursor migration during neocortex development. This could be the mechanism that explains why pathological forms of myoclonin-1 affect brain development. [less ▲]

In search of a physiological role for thiamine triphosphate and the 25-kDa thiamine triphosphatase L. BETTENDORFF, B. LAKAYE, G. KOHN AND P. WINS GIGA-Neurosciences, University of Liège, 4000-Liège ... [more ▼]

In search of a physiological role for thiamine triphosphate and the 25-kDa thiamine triphosphatase L. BETTENDORFF, B. LAKAYE, G. KOHN AND P. WINS GIGA-Neurosciences, University of Liège, 4000-Liège, Belgium Thiamine triphosphate (ThTP) was discovered over 60 years ago. Although it is present in most organisms from bacteria to mammals, its possible biological functions remain unclear. In contrast to thiamine diphosphate (ThDP), it is not a coenzyme. In E. coli cells, ThTP is transiently produced in response to amino acid starvation, while in mammalian cells, it is constitutively produced at a low rate. In some animal tissues, ThTP was able to phosphorylate proteins and activate a high-conductance anion channel in vitro. These observations raised the possibility of ThTP being part of a still uncharacterized cellular signaling pathway. Though it was long thought that ThTP is synthesized by a specific ThDP:ATP phosphotransferase, more recent studies indicate that two main mechanisms are involved: (1) in the cytosol adenylate kinase 1 can catalyze ThTP production from ThDP and ADP and (2) in brain mitochondria FoF1-ATP synthase can catalyze ThTP production from ThDP + Pi. The latter reaction is energized by the respiratory chain through a chemiosmotic mechanism analogous to oxidative phosphorylation. Both mechanisms are conserved from bacteria to mammals. While ThTP synthesis does not seem to require a specific enzyme, its hydrolysis in mammalian tissues is catalyzed by a very specific cytosolic 25 kDa thiamine triphosphatase (ThTPase). Because of this activity, steady-state ThTP levels are kept low in mammalian cells. ThTPase belongs to the CYTH superfamily of proteins which has representatives in all superkingdoms of life acting on tripolyphosphate and various triphosphorylated substrates. Although the whole chromosome region containing the ThTPase gene was lost in birds, orthologs of the ThTPase gene were found in all other known metazoan genomes. It seems that ThTPase activity appeared as a secondary acquisition of the CYTH proteins in the lineage leading from cnidarians to vertebrates. In particular, the Trp-53 residue of mammalian ThTPases plays a key role in substrate recognition and specificity by interacting with the thiazole part of ThTP. This residue is conserved in metazoan CYTH proteins with ThTPase activity. In order to gain insight into the physiological function(s) of the ThTP-ThTPase couple, we tried to produce a mouse invalidated in 25-kDa ThTPase. Surprisingly, we were unable to obtain any knockout animal, apparently because ThTPase seems to be required for spermatogenesis. As we previously showed that the enzyme is much more abundant in differentiated versus undifferentiated cells, we suspect that 25-kDa ThTPase might play a more general and important role during cell differentiation. Acknowledgments This work was supported by the F.R.S.-FNRS. LB and BL are respectively Research Director and Research Associate at the F.R.S.-FNRS. [less ▲]

For many years, our laboratory has been interested in thiamine triphosphate (ThTP), a vitamin B1 derivative whose metabolism and physiological role remain unclear. Regarding its production, we have shown ... [more ▼]

For many years, our laboratory has been interested in thiamine triphosphate (ThTP), a vitamin B1 derivative whose metabolism and physiological role remain unclear. Regarding its production, we have shown that in E. coli and in rat brain mitochondria, ThTP is synthesized from thiamine diphosphate and inorganic phosphate through a chemiosmotic mechanism involving the FoF1- ATP synthase [1, 2]. In mammalian cells, its concentration is maintained at a low level through hydrolysis by a very specific cytosolic 25-kDa thiamine triphosphatase (ThTPase) [3]. In order to gain insight in the role of ThTP and ThTPase in mammalian tissues, we decided to generate a mouse strain invalidated in 25kDa-ThTPase with the hope that these mice will accumulate ThTP in their tissues. We obtained genetically modified embryonic stem (ES) cells from the Knockout Mouse Project (KOMP) repository. In those cells, one of the 25kDa-ThTPase alleles was replaced by a construction containing the lacZ and the neomycin resistance genes. Those ES cells were microinjected in blastocysts and the chimeric blastocysts were injected in a mouse uterus to generate chimerae. However, when we bred those mice with wild type mice, the construction was never transmitted to the pups. To explain this result, we selected those chimerae that presented a sex-reversal. In those mice, all the spermatozoids derive from the injected embryonic stem cells, so that half of the spermatozoids are expected to harbor the construction. However, after qPCR analysis, we observed that the spermatozoids with the construction were outnumbered by a factor of thousand. These results strongly suggest that the 25kDa-ThTPase is required for spermatozoid development. 1. Gangolf, M., Wins, P., Thiry, M., El Moualij, B. & Bettendorff, L. (2010) J. Biol. Chem. 285, 583-94. 2. Gigliobianco, T., Gangolf, M., Lakaye, B., Pirson, B., von Ballmoos, C., Wins, P. & Bettendorff, L. (2013) Scientific reports. 3, 1071. 3. Lakaye, B., Makarchikov, A. F., Antunes, A. F., Zorzi, W., Coumans, B., De Pauw, E., Wins, P., Grisar, T. & Bettendorff, L. (2002) J. Biol. Chem. 277, 13771-7. [less ▲]

In E. coli, thiamine triphosphate (ThTP), a putative signaling molecule, transiently accumulates in response to amino acid starvation. This accumulation requires the presence of an energy substrate yielding pyruvate. Here we show that in intact bacteria ThTP is synthesized from free thiamine diphosphate (ThDP) and Pi, the reaction being energized by the proton-motive force (Dp) generated by the respiratory chain. ThTP production is suppressed in strains carrying mutations in F1 or a deletion of the atp operon. Transformation with a plasmid encoding the whole atp operon fully restored ThTP production, highlighting the requirement for FoF1-ATP synthase in ThTP synthesis. Our results show that, under specific conditions of nutritional downshift, FoF1-ATP synthase catalyzes the synthesis of ThTP, rather than ATP, through a highly regulated process requiring pyruvate oxidation. Moreover, this chemiosmotic mechanism for ThTP production is conserved from E. coli to mammalian brain mitochondria. [less ▲]

Background: Thiamine triphosphate (ThTP) is present in most organisms and might be involved in intracellular signaling. In mammalian cells, the cytosolic ThTP level is controlled by a specific thiamine ... [more ▼]

Background: Thiamine triphosphate (ThTP) is present in most organisms and might be involved in intracellular signaling. In mammalian cells, the cytosolic ThTP level is controlled by a specific thiamine triphosphatase (ThTPase), belonging to the CYTH superfamily of proteins. CYTH proteins are present in all superkingdoms of life and act on various triphosphorylated substrates. Methods: Using crystallography, mass spectrometry and mutational analysis, we identified the key structural determinants of the high specificity and catalytic efficiency of mammalian ThTPase. Results: Triphosphate binding requires three conserved arginines while the catalytic mechanism relies on an unusual lysine-tyrosine dyad. By docking of the ThTP molecule in the active site, we found that Trp-53 should interact with the thiazole part of the substrate molecule, thus playing a key role in substrate recognition and specificity. Sea anemone and zebrafish CYTH proteins, which retain the corresponding Trp residue, are also specific ThTPases. Surprisingly, the whole chromosome region containing the ThTPase gene is lost in birds. Conclusion: The specificity for ThTP is linked to a stacking interaction between the thiazole heterocycle of thiamine and a tryptophan residue. The latter likely plays a key role in the secondary acquisition of ThTPase activity in early metazoan CYTH enzymes, in the lineage leading from cnidarians to mammals. General significance: We show that ThTPase activity is not restricted to mammals as previously thought but is an acquisition of early metazoans. This, and the identification of critically important residues, allows us to draw an evolutionary perspective of the CYTH family of proteins. [less ▲]

Background: We recently characterized a specific inorganic triphosphatase (PPPase) from Nitrosomonas europaea. This enzyme belongs to the CYTH superfamily of proteins. Many bacterial members of this ... [more ▼]

Background: We recently characterized a specific inorganic triphosphatase (PPPase) from Nitrosomonas europaea. This enzyme belongs to the CYTH superfamily of proteins. Many bacterial members of this family are annotated as predicted adenylate cyclases, because one of the founding members is CyaB adenylate cyclase from A. hydrophila. The aim of the present study is to determine whether other members of the CYTH protein family also have a PPPase activity, if there are PPPase activities in animal tissues and what enzymes are responsible for these activities. Methodology/Principal Findings: Recombinant enzymes were expressed and purified as GST- or His-tagged fusion proteins and the enzyme activities were determined by measuring the release of inorganic phosphate. We show that the hitherto uncharacterized E. coli CYTH protein ygiF is a specific PPPase, but it contributes only marginally to the total PPPase activity in this organism, where the main enzyme responsible for hydrolysis of inorganic triphosphate (PPPi) is inorganic pyrophosphatase. We further show that CyaB hydrolyzes PPPi but this activity is low compared to its adenylate cyclase activity. Finally we demonstrate a high PPPase activity in mammalian and quail tissue, particularly in the brain. We show that this activity is mainly due to Prune, an exopolyphosphatase overexpressed in metastatic tumors where it promotes cell motility. Conclusions and General Significance: We show for the first time that PPPase activities are widespread in bacteria and animals. We identified the enzymes responsible for these activities but we were unable to detect significant amounts of PPPi in E. coli or brain extracts using ion chromatography and capillary electrophoresis. The role of these enzymes may be to hydrolyze PPPi, which could be cytotoxic because of its high affinity for Ca2+, thereby interfering with Ca2+ signaling. [less ▲]